Cassette for storing a plurality of semiconductor wafers

ABSTRACT

A cassette for storing a plurality of semiconductor wafers with a space in the vertical direction has a plurality of support plates which are provided spaced apart from one another in the vertical direction. A receiving cut-out having a shape corresponding to the shape of an adsorber for suction-holding a semiconductor wafer are formed in the front half portion of each of the support plates. The cassette further comprises separation plates between adjacent support plates.

FIELD OF TECHNIQUE

[0001] The present invention relates to a cassette for storing aplurality of semiconductor wafers with a space therebetween in thevertical direction.

TECHNICAL BACKGROUND

[0002] As well known to persons skilled in the art, when a semiconductoris ground or cut, a plurality of semiconductor wafers are stored in acassette, and the cassette is carried to a predetermined site. Thecassette has a pair of side walls extending vertically at an intervaltherebetween in the crosswise direction, and in the inner sides of theside walls, support ribs or support grooves are formed with a spacetherebetween in the vertical direction. The semiconductor wafers areeach stored in the cassette by positioning their both edge portions onthe respective support ribs or in the respective support grooves of boththe side walls. Therefore, a plurality of semiconductor wafers arestored with a space therebetween in the vertical direction (the spacecorresponds to an interval between adjacent support ribs or supportgrooves) in the cassette. An adsorber having suction holes in its topsurface is used to carry semiconductor wafers into the cassette or tocarry them out from it. To carry a semiconductor wafer into thecassette, the semiconductor wafer is vacuum adsorbed to the adsorber andcarried to a predetermined position in the cassette, the vacuumadsorption of the semiconductor wafer is then released to leave thesemiconductor wafer in the cassette, and the adsorber is pulled out fromthe cassette. To carry a semiconductor wafer out from the cassette, theadsorber is put into the cassette, positioned under the semiconductorwafer to vacuum adsorb the semiconductor wafer, and then, the adsorbersuction-holding the semiconductor wafer is pulled out from the cassette.

[0003] The above conventional cassette, however, involves the followingproblems. That is, the thickness of each semiconductor wafer is oftenmade extremely small, for example, to 100 μm or less, particularly 50 μmor less, in recent years. When a semiconductor wafer having an extremelysmall thickness is stored in the cassette, it may be bent in a concaveform so that its center portion is liable to be displaced in a downwarddirection. Since the curvature of each semiconductor wafer is not alwaysthe same, when the semiconductor wafer bends, the space in the verticaldirection between adjacent semiconductor wafers stored in the cassettewith a space therebetween in the vertical direction becomes extremelysmall locally. Therefore, there is a possibility that when the adsorberis inserted into the cassette and positioned under the semiconductorwafer, it may bump into the semiconductor wafer and damage thesemiconductor wafer. Further, there is a possibility that when thesemiconductor wafer greatly bends, it may come into contact with anothersemiconductor wafer arranged adjacent thereto in the vertical direction,whereby the semiconductor wafer may be damaged.

[0004] JP-A 2000-91400 discloses a cassette provided with a plurality ofsupport plates arranged with a space therebetween in the verticaldirection to define a plurality of semiconductor wafer storage spaces inthe cassette. Each of the support plates has a cut-out correspondent tothe shape of an adsorber for suction-holding a semiconductor wafer. Inthe cassette, each semiconductor wafer is supported not only at its bothedge portions but also at its center portion, thereby suppressing itscurvature caused by its own weight. As semiconductor wafers adjacent toeach other in the vertical direction are separated from each other bythe support plate, they are not contacted to each other.

[0005] However, the cassette disclosed by the above JP-A 2000-91400remains yet not satisfactory. According to the experience of theinventor of the present invention, a semiconductor wafer which has beenmade very thin by grinding its back surface is bent in a concave orconvex form due to grinding distortion or crystal orientation.Therefore, even when the semiconductor wafer is supported at its bothedge portions and its center portion, the semiconductor wafer is curved.Accordingly, even when the cassette disclosed by JP-A 2000-91400 isused, there still exists a possibility that the adsorber may bump intothe semiconductor wafer and damage it, at the time when the adsorber isinserted into the cassette.

DISCLOSURE OF THE INVENTION

[0006] It is therefore an object of the present invention to provide anovel and improved cassette which prevents a semiconductor wafer frombeing damaged by bumping into an adsorber sufficiently surely when thesemiconductor wafer is carried into, or out from, the cassette even ifthe semiconductor wafer is bent in a concave or convex form.

[0007] According to the present invention, to attain the above object, aplurality of support plates are provided spaced apart from one anotherin the vertical direction and further, separation plates are providedbetween adjacent support plates.

[0008] That is, according to the present invention, there is provided acassette for storing a plurality of semiconductor wafers with a spacetherebetween in the vertical direction, comprising a plurality ofsupport plates which are provided spaced apart from one another in thevertical direction and have a receiving cut-out correspondent to theshape of an adsorber for suction-holding a semiconductor wafer in thefront half portions of the surface plates, wherein

[0009] separation plates are provided between adjacent support plates.

[0010] Preferably, the separation plates are plates having a shapecorrespondent to the shape of the semiconductor wafer.

[0011] Preferably, the cassette comprises a top plate above theuppermost support plate and a bottom plate under the lowest positionalsupport plate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a perspective view of a cassette constituted accordingto the present invention;

[0013]FIG. 2 is a front view of the cassette of FIG. 1;

[0014]FIG. 3 is a perspective view of a support plate in the cassette ofFIG. 1;

[0015]FIG. 4 is a perspective view of a separation plate in the cassetteof FIG. 1;

[0016]FIG. 5 is a sectional view of side walls and rear members of thecassette of FIG. 1;

[0017]FIG. 6 is a perspective view of a typical example of asemiconductor wafer carrying means;

[0018]FIG. 7 are sectional views for explaining how to carry asemiconductor wafer into the cassette of FIG. 1; and

[0019]FIG. 8 are sectional views for explaining how to carry asemiconductor wafer out from the cassette of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] A preferred embodiment of a cassette constituted according to thepresent invention will be described in detail hereinafter with referenceto the accompanying drawings.

[0021] Referring to FIG. 1 and FIG. 2, a cassette denoted by referencenumeral 2 as a whole and constituted according to the present inventioncomprises a top plate 4 and a bottom plate 6. The top plate 4 has asubstantially disk-like shape and an arcuate projection portion 8 atboth sides. Similarly, the bottom plate 6 also has a substantiallydisk-like shape and an arcuate projection portion 10 at both sides. Sidewalls 12 extending vertically are fixed between the projection portions8 of the top plate 4 and the projection portions 10 of the bottom plate6. A pair of rear members 14 extending vertically are secured to therear ends of the top plate 4 and the bottom plate 6 at an intervaltherebetween. Grip members 16 having a channel-like cross section arefixed on the respective projection portions 8 of the top plate 4. Tocarry the cassette 2 manually or by a proper carrying means (not shown),the grip portions 16 may be held.

[0022] A plurality of (5 plates in the illustrated embodiment) ofsupport plates 18 are provided, with a predetermined space therebetweenin the vertical direction, between the top plate 4 and the bottom plate6. Separation plates 20 are provided between each of adjacent supportplates 18. Describing in more detail with reference to FIGS. 3 to 5together with FIG. 1 and FIG. 2, a plurality of (9 pieces in theillustrated embodiment) of support ribs 22 are formed on the inner sidesof the side walls 12 with a predetermined space therebetween in thevertical direction. Similarly, a plurality of (9 pieces in theillustrated embodiment) of support ribs 24 are formed on the inner sidesof the rear members 14 with a predetermined space therebetween in thevertical direction. The support plates 18 are situated at predeterminedpositions by fixing their peripheries on odd-numbered ribs 22 and 24from the top, and the separation plates 20 are situated at predeterminedpositions by fixing their peripheries on even-numbered ribs 22 and 24from the top. As clearly shown in FIG. 3, each of the support plates 18is substantially semicircular, its both side portions are made linearalong the inner surfaces of the side walls 12, and a receiving cut-out26 correspondent to the shape of an adsorber to be described later areformed in its front half portion. As shown in FIG. 4, each of theseparation plates 20 has a substantially disk-like shape correspondentto the shape of the semiconductor wafer, and its both side portions aremade linear along the inner surfaces of the side walls 12.

[0023] The cassette 2 as described above can be manufactured favorablyby forming its constituent elements (that is, the top plate 3, bottomplate 6, side walls 12, rear members 14, grip members 16, support plates18 and separation plates 20) from a synthetic resin or metal sheet andjoining them together by a suitable means such as an adhesive.

[0024]FIG. 6 shows a typical example of a semiconductor wafer carryingmeans 28 used to carry a semiconductor wafer into, and out from, thecassette 2. The illustrated semiconductor wafer carrying means 28 whichis known per se comprises a lift shaft 32 mounted on a base 30 so as tobe able to ascend and descend, a first swing arm 34 rotatably mounted onthe top end of the lift shaft 32, a second swing arm 36 rotatablymounted on the end of the first swing arm 34, a mounting block 38secured to the end of the second swing arm 36, and an adsorber 42turnably mounted to the mounting block 38 on a central axis 40 extendingsubstantially horizontally as the center. The illustrated adsorber 42has a bifurcate fork-like form, and porous suction pieces 46 are formedin the respective suction surfaces (top surfaces in FIG. 6) of twofingers 44. Another suitable adsorber may be used as desired, and it isimportant that the shape of the receiving cut-out 26 in the supportplate 18 should correspond to the shape of the adsorber in use. Thesemiconductor wafer carrying means 28 is provided with a lifting means(not shown) for vertically moving the lift shaft 32, the first swingingmeans (not shown) for swinging the first swing arm 34, the secondswinging means (not shown) for swinging the second swing arm 36 and arotary means (not shown) for rotating the adsorber 42. Further, it isfurther provided with a suction means for communicating the suctionpieces 46 of the adsorber 42 with a vacuum source selectively.

[0025] The semiconductor wafer 48 has a substantially disk-like shapeand a linear edge 50 called “orientation flat” at part of its periphery.To carry the semiconductor wafer 48 by the semiconductor wafer carryingmeans 28, the suction surface of the adsorber 42 is brought into a closecontacted with one side of the semiconductor wafer 48 to communicate thesuction pieces 46 with the vacuum source, thereby causing the adsorber42 to adsorb the semiconductor wafer 48.

[0026] For instance, to pickup the semiconductor wafer 26 whose backsurface has been ground, from a chuck means of a grinding machine (notshown), the adsorber 42 of the semiconductor wafer carrying means 28 isrotated at 180° from the state shown in FIG. 6 to direct the suctionsurface having the suction pieces 46 downward. The suction surface ofthe adsorber 42 is pressed against the faced-up back side of thesemiconductor wafer 48 on the chuck means to adsorb the semiconductorwafer 48 thereto.

[0027]FIG. 7 show an example of how to carry the semiconductor wafer 48that has been adsorbed to the adsorber 42, onto the support plate 18locating at the uppermost top position of the cassette 2. To carry thesemiconductor wafer 48 into the cassette 2, after the semiconductorwafer 48 is adsorbed to the suction surface of the adsorber 42 and takenout from the chuck means, the adsorber 42 is rotated at 180° to directthe suction surface adsorbing the semiconductor wafer 48 upward.Thereafter, as shown in FIG. 7(A), the adsorber 42 and the semiconductorwafer 48 adsorbed to the suction surface thereof are inserted into thecassette 2 by aligning the two fingers 44 of the adsorber 42 with therespective receiving cut-out 26 of the support plate 18 and positioningthe semiconductor wafer 48 above the support plate 18. Subsequently, thesuction pieces 46 of the adsorber 42 are disconnected from the vacuumsource and opened to the air to stop the adsorption of the semiconductorwafer 48. Then, the adsorber 42 is lowered. When the adsorber 42 islowered up to the position shown in FIG. 7(B), the semiconductor wafer48 is placed on the support plate 18. When the adsorption of thesemiconductor wafer 48 by the suction pieces 46 is stopped, if thesemiconductor wafer 48 is extremely thin, for example as shown in FIG.7(B), it tends to be bent in a concave form (or in a convex form inreverse) due to grinding distortion or crystal orientation. Then, asshown in FIG. 7(C), the adsorber 42 is further lowered a bit to separatethe semiconductor wafer 48 placed on the support plate 18 therefromcompletely. Thereafter, the adsorber 42 is pulled out from the cassette2. The semiconductor wafer 48 can be carried onto support plates 18other than the uppermost top support plate 18 in the same manner asabove.

[0028]FIG. 8 show an example of how to carry the semiconductor wafer 48placed on the uppermost top support plate 18 out from the cassette 2.First, as shown in FIG. 8(A), the adsorber 42 is inserted, in a state ofits suction surface face up being maintained, between the uppermostsupport plate 18 and the separation plate 20 positioned under thesupport plate 18. Then, as shown in FIGS. 8(B) and 8(C), the adsorber 42is moved up through the receiving cut-out 26 of the support plate 18.When the adsorber 42 is moved up to the position shown in FIG. 8(C), thesemiconductor wafer 48 is pressed against the inner side of the topplate 4 (in the case of a semiconductor wafer 48 positioned under thesupport plate 18, it is pressed against the inner side of the separationplate 20 positioned above the support plate 18), whereby the curvatureof the semiconductor wafer 48 is corrected to make the semiconductorwafer 48 into a flattened state. Thereafter, the suction pieces 46 ofthe adsorber 42 are communicated with the vacuum source to adsorb thesemiconductor wafer 48 to the suction surface. Then, the adsorber 42 isslightly lowered to separate the semiconductor wafer 48 from the innerside of the top plate 4 (or the separation plate 20) and pulled out fromthe cassette 2 while adsorbing the semiconductor wafer 48.

[0029] In the embodiment shown in FIG. 7 and FIG. 8, the adsorber 42adsorbing the semiconductor wafer 48 is inserted into the cassette 2 ina state of its suction surface face up to place the semiconductor wafer48 on the support plate 18 of the cassette 2, and when the semiconductorwafer 48 on the support plate 18 is carried out from the support plate18, too, the adsorber 42 is inserted into the cassette 2 in a state ofits suction surface face up. However, as required, the adsorber 2adsorbing the semiconductor wafer 48 may be inserted into the cassette 2in a state of its suction surface face down, that is, in a state of thesemiconductor wafer 48 being adsorbed to the under side of the adsorber42, and placed on the separation plate 20 positioned under the supportplate 18 and not on the support plate 18. In this case, to carry thesemiconductor wafer 48 placed on the separation plate 20 out from thecassette 2, the adsorber 42 may be inserted into the cassette 2 in astate of its suction surface face down.

[0030] While the preferred embodiment of the cassette constitutedaccording to the present invention has been described in detail withreference to the accompanying drawings, the present invention is notlimited to the above embodiment and it should be understood that variouschanges and modifications can be made without departing from the spiritand scope of the invention.

1. A cassette for storing a plurality of semiconductor wafers with aspace therebetween in the vertical direction, comprising a plurality ofsupport plates which are provided spaced apart from one another in thevertical direction and have a receiving cut-out correspondent to theshape of an adsorber for suction-holding a semiconductor wafer in thefront half portions of the support plates, wherein separation plates areprovided between adjacent support plates.
 2. The cassette of claim 1,wherein the separation plates are plates having a shape nearlycorrespondent to the shape of the semiconductor wafer.
 3. The cassetteof claim 1, which comprises a top plate above the uppermost supportplate and a bottom plate under the lowest positional support plate.